1. Technical Field
The present disclosure relates to a display apparatus; in particular, to a method for adjusting gamma curve for a display control system and a gamma voltage generator thereof.
2. Description of Related Art
Display technology is currently undergoing rapid evolvement. The liquid crystal display (LCD) is widely utilized as an image output apparatus for various electronic devices. A liquid crystal particle in the LCD rotates according to an applied voltage, for controlling transmittance of a corresponding sub-pixel.
Please refer to FIG. 1. FIG. 1 is a partial block diagram illustrating a conventional display control system. As shown in FIG. 1, a gamma voltage generator 11 of the conventional display control system receives a system voltage AVDD and generates a plurality of gamma reference voltages VGMA—1˜VGMA—N according to a plurality of resistors 112 coupled in series. A gray level voltage generator 122 of a source driving circuit 12 in the conventional display control system generates gray level voltages Vg1˜Vgn according to the plurality of gamma reference voltages VGMA—1˜VGMA—N respectively.
As shown in FIG. 1, the gray level voltages Vg1˜Vgi are generated according to the gamma reference voltages VGMA—1˜VGMA—2. The gray level voltages Vgk˜Vgn are generated according to the gamma reference voltages VGMA—N-1˜VGMA—N. Similarly, other gray level voltages can be generated according to two consecutive gamma reference voltages VGMA—i-1˜VGMA—i. Subsequently, the conventional display control system generates a plurality of control signals X1˜XL according to a sub-pixel gray value of each sub-pixel respectively. The source driving circuit 12 receives the control signals X1˜XL corresponding to the respective sub-pixels. The source driving circuit 12 then selects one of the gray level voltages Vg1˜Vgn as a driving voltage Y1˜YL for each corresponding sub-pixel, according to the respective control signals X1˜XL received, so as to control a rotation of each corresponding liquid crystal.
Please refer to FIG. 2. FIG. 2 is a diagram illustrating a gamma curve corresponding to a conventional liquid crystal display panel. As shown in FIG. 2, the vertical axis represents driving voltages corresponding to liquid crystals of the sub-pixels and the horizontal axis represents gray values corresponding to the sub-pixels. Since resistances of the plurality of resistors 112 coupled in series are constant, voltage values of the gamma reference voltages VGMA—1˜VGMA—N are also constant which cannot be adjusted so the gamma curve cannot be adjusted either.
Generally, human eyes are more sensitive to details in the dark than in the light. Hence a gray level voltage number corresponding to a plurality of sub-pixels with relatively large gray values is relatively small (i.e. quantized to a relatively lesser extent), and a gray level voltage number corresponding to a plurality of sub-pixels with relatively small gray values is relatively large (i.e. quantized to a relatively greater extent), for maintaining display saturation of a frame.
For maintaining display saturation of the frame, resistances of the plurality of resistors 112 can be designed in a manner such that a larger voltage difference exists between two consecutive gamma reference voltages VGMA —1˜VGMA—2. A gray level voltage number corresponding to a plurality of sub-pixels with relatively large gray values is therefore decreased (i.e. quantized to a relatively lesser extent), and a gray level voltage number corresponding to a plurality of sub-pixels with relatively small gray values is increased (i.e. quantized to a relatively greater extent).
Take FIG. 2 as an example. Sub-pixels with gray values 255˜176 can correspond to 10 gray level voltages generated by two consecutive gamma reference voltages VGMA—1˜VGMA—2 with a larger voltage difference. On the other hand, sub-pixels with gray values 44˜0 can correspond to 10 gray level voltages generated by two consecutive gamma reference voltages VGMA—N-1˜VGMA—N with a smaller voltage difference.
However, since gray values of a plurality of sub-pixels of a frame can concentrate towards a certain value range, if the gamma curve or the gamma reference voltages VGMA—1˜VGMA—N cannot be dynamically adjusted, contrast of the frame is deteriorated, consequently lowering the display quality.